Component: Modem

This component is provided by network cards. Wireless network cards behave much like normal network cards, but additionally send the message as a wireless “packet” when a strength is set. The modem's address must be used for networking. It can be found through component.modem.address.

Component name: modem.

  • isWireless(): boolean
    Returns whether this modem is capable of sending wireless messages.
  • maxPacketSize(): number
    Returns the maximum packet size for sending messages via network cards. Defaults to 8192. You can change this in the OpenComputers configuration file.
    Every value in a message adds two bytes of overhead. (Even if there's only one value.)
    Numbers add another 8 bytes, true/false/nil another 4 bytes, and strings exactly as many bytes as the string contains—though empty strings still count as one byte.
    • "foo" is a 5-byte packet; two bytes of overhead and a three byte string.
    • "currentStatus",300 is a 25-byte packet; four bytes overhead, a 13-byte string, and 8 bytes for a number.
  • isOpen(port: number): boolean
    Returns whether the specified “port” is currently being listened on. Messages only trigger signals when they arrive on a port that is open.
  • open(port: number): boolean
    Opens the specified port number for listening. Returns true if the port was opened, false if it was already open. Note: maximum port is 65535
  • close([port: number]): boolean
    Closes the specified port (default: all ports). Returns true if ports were closed.
  • send(address: string, port: number[, ...]): boolean
    Sends a network message to the specified address. Returns true if the message was sent. This does not mean the message was received, only that it was sent. No port-sniffing for you.
    Any additional arguments are passed along as data. These arguments must be basic types: nil, boolean, number and string values are supported, tables and functions are not. See the serialization API for serialization of tables.
    The number of additional arguments is limited. The default limit is 8. It can be changed in the OpenComputers configuration file, but this is not recommended; higher limits can allow relatively weak computers to break relatively strong ones with no defense possible, while lower limits will prevent some protocols from working.
  • broadcast(port: number, ...): boolean
    Sends a broadcast message. This message is delivered to all reachable network cards. Returns true if the message was sent. Note that broadcast messages are not delivered to the modem that sent the message.
    All additional arguments are passed along as data. See send.
  • getStrength(): number
    The current signal strength to apply when sending messages. Wireless network cards only.
  • setStrength(value: number): number
    Sets the signal strength. If this is set to a value larger than zero, sending a message will also generate a wireless message. The higher the signal strength the more energy is required to send messages, though. Wireless network cards only.
  • getWakeMessage():string
    Gets the current wake-up message.
  • setWakeMessage(message: string):string
    Sets the wake-up message to the specified string.

This component generates a signal named modem_message if a message from another network card is received.
It has the signature localAddress: string, remoteAddress: string, port: number, distance: number, ....

  • localAddress is the address of the modem component the message was received by.
  • remoteAddress is the address of the network card the message was sent from.
  • port is the port number the message was delivered to.
  • distance is the distance to the modem that sent the message. This is only set for wireless messages. For normal messages this is always 0.
  • All further values are values passed along by the sender (i.e. the ... in send and broadcast).

Example use:

local component = require("component")
local event = require("event")
local m = component.modem -- get primary modem component
print(m.isOpen(123)) -- true
-- Send some message.
m.broadcast(321, "this is a test")
-- Wait for a message from another network card.
local _, _, from, port, _, message = event.pull("modem_message")
print("Got a message from " .. from .. " on port " .. port .. ": " .. tostring(message))